The present invention relates generally to downhole acoustic communication systems and, in an embodiment described herein, more particularly provides an acoustic probe conveyed on a wireline to facilitate calibration and communication in an acoustic communication system.
It is well known to communicate acoustically downhole by transmitting acoustic signals through a tubular string positioned in a wellbore of a well. Components of an acoustic communication system are typically interconnected in the tubular string, so that the components communicate with each other by transmitting acoustic signals through the tubular string extending between the components. The tubular string between the components may be made up of various tubular elements having, for example, differing wall thickness, length, etc. In addition, for different wells with different spacings between the components, the number of connections in the tubular string between the components varies.
Unfortunately, the variations in the tubular string material, length, number of connections, etc., between the components makes it difficult to determine beforehand an optimum frequency for acoustic communication between the components. One aspect of the difficulty is that, prior to interconnecting the acoustic communication system in the tubular string, the variations in the tubular string may not be known. Furthermore, after the tubular string has been installed in the well, with the acoustic communication system interconnected therein, it may not be possible to make adjustments to the acoustic frequency used for transmission in the system, and so a preselected frequency must be used, even though it is less than optimum.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, an acoustic communication system is provided which utilizes an acoustic wireline probe. Associated methods are also provided.
In one aspect of the present invention, the acoustic probe is capable of acoustically communicating with components of a downhole acoustic communication system interconnected in a tubular string positioned in a well. For this purpose, the probe may include a piezoelectric device for transmitting acoustic commands to the system components. In addition, the probe may include an accelerometer for receiving acoustic signals transmitted from the system components.
In another aspect of the present invention, the probe may be utilized in a method of calibrating the communication system. For example, the probe may be positioned proximate a transmitter of the system and the probe may acoustically command the transmitter to generate acoustic frequency sweeps. The probe may then be positioned proximate a receiver of the system, where the probe receives the frequency sweeps. The received frequency sweeps may be analyzed to determine an optimum frequency for communication between the transmitter and the receiver. The probe may then be positioned proximate the transmitter, where the probe commands the transmitter to use the optimum frequency for subsequent communication with the receiver. In this manner, the system may be calibrated so that it uses the optimum frequency for acoustic communication, after the system has been installed in the well.
In another aspect of the present invention, the probe has the capability of transmitting acoustic signals received by it in either analog or digital form. For example, it may be desirable, for diagnostic purposes, for an operator at the surface to be able to hear the xe2x80x9crawxe2x80x9d acoustic signals received by the probe downhole. This is accomplished by the probe transmitting the received acoustic signals via a wireline in analog electrical form. Where a digital form of received acoustic signals is desired, such as for data analysis, the probe may include an onboard digital signal processor, so that the received acoustic signals are transmitted via the wireline in digital electrical form.
In still another aspect of the present invention, the acoustic communication system is configured in a unique manner which facilitates its use with the probe. The transmitter is interconnected in the tubular string above a packer and a valve in the string. In this manner, even though the valve may be closed, preventing fluid flow through the tubular string, the probe may still be positioned proximate the transmitter for communication therewith, and communication with other components in the string is enhanced. The transmitter may include a sensor sensing a property of a fluid disposed below the packer.